Process for the production of hard carbides



Patented May 16, 1939 UNITED STATES PATENT OFFICE Oskar Meyer, Bitterfeld, Germany, assignor to I. G. Farhenindustrie Aktiengesellschaft,

Frankfort-on-the-Main, Germany No Drawing. Application January 23, 1937, Se-

rial N 0. 122,007.

1 Claim.

This invention relates to a process for the production of hard carbides, and more particularly titanium carbide, free from graphite.

The known process for producing titanium carbide by heating a mixture of titanium oxide, or other titanium compounds, with carbon, in which it is necessary to employ temperatures of 1800 C. and over, in order to obtain the most complete reduction possible, invariably furnishes f products containing certain amounts of free carbon, in the form of graphite, which is highly undesirable, especially when said titanium carbide is employed for the production of hard metal.

I The same applies to the other carbides employed for the production of hard metal.

In order to eliminate this content of graphite, it has been proposed to effect the reduction and carburisation by stages, in a plurality of working operations, the reaction mixture being arranged to contain the optimum carbon content in each case. An attempt has also been made to convert the uncombined carbon into tungsten carbide, or tungsten-titanium carbide, by heating the g5 carbon-laden carbide in one or more operations, with predetermined quantities of tungsten at temperatures in the vicinity of 1800 C., so as to obtain a double carbide, free from graphite, suitable for the production of complex hard-metal compounds. Finally, unsuccessful attempts have been made to separate the graphite from the carbide, by wet mechanical treatment such as elutriation and the like.

The present invention aims at obviating the drawbacks inherent in the foregoing processes and to this end the invention provides a process for combining the free carbon occurring in the production of hard carbides, titanium carbide in particular, with metals which, on the one hand,

have a tendency to form carbides more rapidly and completely and on the other hand, yield carbides which can be easily extracted from the resulting carbide mixture by treatment with chemical solvents.

In accordance with the present invention hard carbides containing free carbon are, for the purpose of removing such free carbon, treated with manganese so as to cause such manganese to 60 form manganese carbide with the free carbon.

The manganese carbide contained in the resultant mixture of carbides is thereafter easily decomposed by a treatment of the mixture with acids with liberation of hydrocarbons.

55 If, for example, a mixture of graphite-bearing In Germany February 11,

titanium carbide be heated, at temperatures of only 850-900 C., with a moderate excessreferred to its content of free graphiteof powdered manganese, the carbide MnzC formed from j the free carbon and the manganese powder, can m be easily extracted from the carbide mixture by means of dilute mineral acids, because titanium carbide is practically unaffected thereby, whereas, on the other hand, manganese carbide is completely decomposed, with formation of acetylene 1] C2H2 and methane CH4. Thus, the free carbon absorbed from the crude titanium carbide by the manganese, to form carbide, is eliminated in the form of a gas, whilst the manganese passes, as such, into solution and can be separated from the undecomposed titanium carbide in any convenient manner, such as suction filtration and washmg.

In decomposing the carbon mixture it is preferable to operate with an excess of free acid, because the presence of metal ions, in considerable concentration, in the acid employed for the decomposition easily results in the metallic carbide being only partially decomposed with an undesirable deposition of graphitic carbon.

Example I 325 grms. of a titanium carbide, containing 2.7% of free carbon, were heated with 200 grms. o of manganese powder at 850 C, for 2 hours in an atmosphere of hydrogen. The reaction product was washed with 1250 cc. of dilute (24%) sulphuric acid and subsequently with water, which reduced the content of free carbon to 0.24%. 85

Example II 65 grms. of titanium carbide, containing 1.3% of free carbon, were heated, as above, at 900 C. with 50 grms. of manganese powder, the result- 40 ing product being stirred up with dilute sulphuric acid. A titanium carbide containing only 0.08% of free carbon was obtained.

I claim:

A process for the removal of graphite contained as an impurity in crude hard carbides, which comprises heating the crude carbide containing surplus carbon with manganese to temperatures of between about 850 and about 900 C. so as to cause the surplus carbon to react with the manganese with formation of manganese carbide and thereafter decomposing the manganese carbide formed by treating the carbide mixture with acids.

OSKAR MEYER. ll 

